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Home , Glossotherium, Megalonychidae, Mylodontidae, Paramylodon

Mastozoología Neotropical ISSN: 0327-9383 [email protected] Sociedad para el Estudio de los Mamíferos Argentina

McAfee, Robert K.; Naples, Virginia L. NOTICE ON THE OCCURRENCE OF SUPERNUMERARY TEETH IN THE TWO-TOED Choloepus didactylus AND C. hoffmanni Mastozoología Neotropical, vol. 19, núm. 2, julio-diciembre, 2012, pp. 339-344 Sociedad Argentina para el Estudio de los Mamíferos Tucumán, Argentina

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How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Mastozoología Neotropical, 19(2):339-344, Mendoza, 2012 ISSN 0327-9383 Versión on-line ISSN 1666-0536 ©SAREM, 2012 http://www.sarem.org.ar

NOTICE ON THE OCCURRENCE OF SUPERNUMERARY TEETH IN THE TWO-TOED SLOTHS Choloepus didactylus AND C. hoffmanni

Robert K. McAfee1and Virginia L. Naples2

1 Ohio Northern University, Department of Biological & Allied Health Sciences, 525 S. Main St. Ada, OH 45810, USA [Correspondence: ]. 2 Northern Illinois University, Department of Biological Sciences, Montgomery Hall, DeKalb, IL 60115 USA.

ABSTRACT: Supernumerary teeth occur in nearly all modern mammalian orders, although no previous cases have been published for extant pilosans. We report here three specimens of the genus Choloepus, two C. hoffmanni and one C. didactylus, exhibiting super- numerary teeth. All duplicated teeth are maxillary, and all but one on the right side. One C. hoffmanni bears an additional left tooth, suggesting duplication is neither nor toothrow-side specific. Sloth teeth erupt as simple rounded cones and the different “cusp” patterns characteristic of each extant and extinct genus arise from wear and the differential spacing of upper versus lower dentitions.

RESUMEN: Noticias sobre la ocurrencia de dientes supernumerarios en perezosos de dos dedos, Choloepus didactylus y C. hoffmanni. Si bien casi todos los órdenes de mamíferos modernos presentan dientes supernumerarios, no se habían publicado casos entre pilosos vivientes. En este estudio se documentan dientes supernumerarios en tres individuos del género de perezosos Choloepus: dos C. hoffmani y un C. didactylus. Todos los dientes duplicados se encuentran en el maxilar derecho. Uno de los dos C. hoffmani presenta, además, un diente duplicado del lado izquierdo, lo que sugiere que la duplicación no es específica a nivel de taxón o lateralidad. Los dientes de los perezosos erupcionan como conos simples redondeados y, por lo tanto, la variedad de patrones cuspidales característicos de cada género se produce por el desgaste y el desplazamiento en el espacio de las denticiones superior e inferior.

Key words. Choloepus. Dental anomaly. . Supernumerary teeth. .

Palabras clave. Anomalía dentaria. Choloepus. Dientes supernumerarios. Xenarthra. Megalonychidae.

Members of the Xenarthra (Order Cingulata: afer), by lacking an enamel covering on the , glyptodonts, pampatheres; Order teeth (Shoshani et al., 1988). Instead, the teeth : , sloths), have long been are composed of two layers of dentine, a soft regarded as noteworthy among mammalian inner region of orthovasodentine and a harder species for the uniqueness of their dentition, outer layer of orthodentine, both of which both in structure and dental formula. The are surrounded by a covering of cementum tooth- bearing members of this group (anteat- (Ferigolo, 1985; Kalthoff, 2011). Like those of ers are edentulous) stand out from all other the aardvark, xenarthran teeth are ever-growing, , except the aardvark (Orycteropus high crowned but differ in dental formula and

Recibido 13 junio 2012. Aceptado 14 agosto 2012. Editor asociado: A Abba 340 Mastozoología Neotropical, 19(2):339-344, Mendoza, 2012 RK McAfee and VL Naples http://www.sarem.org.ar dentine structure (Schmidt and Keil, 1971). The among numerous groups, mostly on dental formula in aardvarks is 0.0.2-3.3/0.0.2.3 the basis of the presence of extra or supernu- (Shoshani et al., 1988), whereas no dental for- merary teeth (Drehmer et al., 2004; Loch et al., mula exists for xenarthrans because their teeth 2010). The occurrence of supernumerary teeth do not correspond with or have a known ho- has been well documented in extant members mology to the typical dental classification used of all mammalian orders (at least those that for mammals, i.e., incisors, canines, premolars possess teeth; e.g. Suborder Vermilingua is and molars. The dentine of aardvarks is also edentulous) (Wolsan, 1984) but this particular unique to that taxon and is unlike that of any dental anomaly has not been observed in either other mammals or , whereas that of of the two extant sloth genera until now. Here xenarthrans is similar to the orthodentine of we present the first examples of supernumerary other mammals but with some modifications teeth in the dentition of members of the extant (Schmidt and Keil, 1971). Among sloths, the tree sloth genus Choloepus. teeth are often referred to as being molariform Specimens of Choloepus spp. (77 total) were or caniniform, based on their shapes and loca- examined from the collections of the Division tions along the toothrow. of Mammals of the Field Museum of Natural The dental formula also varies between History (FMNH) and the Kansas Museum of the cingulates and tooth-bearing pilosans. Natural History (KU). The specimens were Cingulate taxa tend to have a high number all wild-caught and excluded zoo specimens. of teeth in the four dental quadrants with the In total, only three specimens exhibited the extant forms ranging from as low as 7-8/8 supernumerary condition for a 3.89% oc- to as high as 18/19 (Wetzel, 1985a, 1985b). currence rate (2/54 from FMNH: 35738 and The sloths, on the other hand, are united by a 41503; 1/23 from KU: 115214). Both species, drastic reduction in the number of teeth, with Choloepus didactylus (Linnaeus’s two-toed most having a generalized formula of either sloth) and Choloepus hoffmanni (Hoffmann’s 4/4, 4/3, or 5/4 (Pujos et al., 2011). Reduction two-toed sloth) exhibit the condition, and all in tooth number is a common character among supernumerary teeth are located in the right sloths, with the two genera of extant tree sloths maxillary toothrow. The exception to this is (the three-toed sloth, Bradypus, and the two- KU 115214 (C. hoffmanni from Nicaragua) toed sloth, Choloepus) possessing a 5/4 dental which has supernumerary teeth in both the left formula. Tooth number and lack of enamel are and right maxillary toothrows. Supernumerary the only commonalities between the two sloth teeth are designated with a ‘d’ prior to the taxa, as the two-toed sloths display the typical abbreviation for the molariform position; i.e., megalonychid condition of a triangular anterior dM1 for a duplicate/supernumerary first upper tooth (caniniform) separated from the posterior molariform. molariforms by a diastema; a feature lacking The lone supernumerary tooth observed in in three-toed sloths. Instead, the anterior teeth C. didactylus (FMNH 41503: Ecuador) is an in three-toed sloths are relatively smaller than adult that is also missing one tooth in the up- the anterior caniniforms of two-toed sloths, and per right series (Fig. 1 A-B), but the remaining are peg or chisel-shaped (Naples, 1982, 1995). teeth and the empty alveolus demonstrate that Molecular data, as well as historical anatomi- the duplication is of either M1 or M2. Regard- cal studies, have shown the close relationship less of the exact tooth position, the posterior between the cingulates and pilosans, with a portion of the toothrow has been crowded and divergence of the two groups at around 65 pushed slightly posteriorly. The right denti- million ago (Delsuc et al., 2002, 2004), tion of the mandibular toothrow is likewise indicating that sloths came from an ancestral affected with a gap occurring between m1 stock with a dental formula including a larger and m2 (Fig. 1 C), as a result of the posterior number of teeth. Changes in dental formulae displacement of the latter. The m2 also lacks have been used to analyze the relationships the typical pointed appearance of Choloepus SUPERNUMERARY TEETH IN Choloepus 341

Fig. 1. Skull and mandible of Choloepus didac- tylus (FMNH 41503) in right lateral (A and C) and ventral (B) views. The supernumerary tooth position is difficult to differentiate between the second or third maxillary molariform on the right side (B). Scales = 10 mm. molariform wear facets (Naples, 1982, 1995); instead resembling more of a roughened plateau with a slight slant along the most anterior and posterior edges. The wear facet morphology of m2 matches that of M3, which occludes directly with the tooth (Fig. 1 A), as opposed to being offset anteriorly by a half tooth length as in the typical sloth tooth spacing arrangement. M3 also bears a cusp anterolabially instead of posteriorly. In the Peruvian specimen of C. hoffmanni (FMNH 35738), the extra tooth appears to be a duplication of M1, occurring just anterior to the actual M1, based upon the orientation of the tooth (Fig. 2 A-B). In Choloepus, as in a number of other sloths genera, M1 is recurved posteriorly so that the wear facet also faces obliquely and posteriorly to contact the anterior edge of m1. The dM1 in this specimen is not recurved, and the oblique wear facet faces anteriorly, where it comes into occlusion with the posterior edge of c1 due to the oppositely oriented wear facets; dM2 (Fig. 2 A), giving the lower caniniform two nearly touches the posterior edge of M1, faces wear facets (Fig. 2 C). The remainder of the anteriorly, and occludes with the posterior m1 dentition exhibits the normal wear patterns facet; M2 proper faces posteriorly and oc- associated with Choloepus, with the exception cludes with the anterior facet of m2. The right of the lower left molariforms where the cusps mandibular dentition has the typical Choloepus are greater on the lingual side instead of the morphology (Fig. 4 B-C). The supernumerary labial. left dM1 occurs anterior to M1 proper and is KU 115214 is a juvenile C. hoffmanni, conical in shape with only the slightest portion based on the simplicity of cranial sutures and of the tip showing any sort of wear (Fig. 3 the lack of their closure/fusion (Figs. 3 and 4 B). All other teeth in the series, maxillary and A). This specimen also stands out by having mandibular, appear unchanged in morphology a duplicate tooth in both upper toothrows; an (Fig. 4 A-C). extra right M2 and a left M1 (Fig. 4 A). On Various dental anomalies are common among the right side, dM2 abuts posteriorly with the mammals (Miles and Grigson, 1990; Wolsan, anterior edge of the proper M2, such that both 1984) and with the above specimens, a supernu- together have a pointed appearance (Fig. 3 A) merary tooth condition is now demonstrated as 342 Mastozoología Neotropical, 19(2):339-344, Mendoza, 2012 RK McAfee and VL Naples http://www.sarem.org.ar

Fig. 2. Skull and mandible of Choloepus hoff- manni (FMNH 35738) in occlusion in right lateral view (A), with dM1 visible in contact with the posterior aspect of C1. The ventral view of the skull (B) and the left dorsolateral view of the mandible (C) are positioned to better illustrate the dental wear features of the maxillary and mandibular teeth. Scales = 10 mm.

This adontia has so far been confined or noted only in some members of the subfamily Mylodontinae; specifically in the Plio- genera of from and from (McAfee, 2007, 2009). It remains to be seen what other dental anomalies are present within the group and what effects they would have had upon the feeding behaviors in those individuals. To conclude, herein is presented the first documented cases of super- numerary teeth in the extant members of the mammalian Order Pilosa. The supernumerary condition currently occurs only within the two species of two-toed sloths, C. didactlyus and C. hoffmanni. Sloth dental morphol- ogy arises from the unique contact wear by the occluding teeth and the half-tooth length offset of the spacing of the upper and lower dentitions. Additional teeth disrupt these relation- ships and may alter the orientation of occurring in all tooth-bearing orders. The three the typical anterolingual masticatory power specimens of Choloepus exhibit additional teeth stroke in these . It remains to be in their maxillary dentition, without restric- seen what effect the changes in tooth posi- tion to a specific species level of occurrence. tion have upon the dental morphologies and Interestingly, the supernumerary condition in subsequent feeding mechanics, and additional sloths appears to be an artifact of the Family research is required to determine whether Megalonychidae, as one occurrence has been this and other dental anomalies also occur noted in the extinct genus , in in three-toed sloths. which the additional tooth was also restricted to the maxillary dentition (McDonald, 1978; Acknowledgements. The authors are thankful to W. Stanley Miles and Grigson, 1990). Of the numerous of the Field Museum and R. Timm of the University of other extinct sloth taxa, no other genus has Kansas for access to the mammalogy collections and their assistance. Thanks also to A. Calvo and A. Cordoba for demonstrated a supernumerary condition. The translational assistance. This manuscript benefitted from only tooth number modification in the extinct the comments and suggestions by reviewers J. Green forms has been the loss of a tooth (adontia). and F. Galliari. SUPERNUMERARY TEETH IN Choloepus 343

Fig. 3. Occluded skull and mandible of Choloepus hoffmanni (KU 115213) in right (A) and left (B) lateral views, illustrating the supernumerary teeth in both toothrows. Scales = 10 mm.

Fig. 4. Ventral view of the skull (A) and lateral views of the mandible (B and C) of C. hoffmanni (KU 115214), to further demonstrate the dental morphologies and wear facets of all the teeth. Scales = 10 mm. 344 Mastozoología Neotropical, 19(2):339-344, Mendoza, 2012 RK McAfee and VL Naples http://www.sarem.org.ar

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